Method And Device For The Electrophoretic Production Of Sheet-Like Blanks From A Metal Slurry Or Ceramic Slip

ABSTRACT

The invention makes it possible to produce very thin ceramic blanks as a precursor for ceramic discs, for example for use as faces in wrist watches. On the other hand, the production of metal blanks for use in CAD/CAM machines is possible with the invention. Both methods are based on depositing the material from a slurry or slip by electrophoresis. The essence of the invention is the isolation of the peripheral region of the precipitation electrodes that is produced by a non-conducting frame. This allows the precipitated mass to be easily lifted off from the precipitation electrode. The subsequent sintering with a possibly proceeding machining operation allows precision articles to be produced.

The invention relates to a method and an apparatus for the production ofelectrophoretic flat blanks from a metal or ceramic slurry.

STATE OF THE ART

The preparation of sinterable precursors by electrophoresis of slurry iswell known in the dental art. As an example, for the production of metalframes that are first prepared by electrophoretic deposition of a metalslurry followed by sintering, refer to DE 10 2005 052 113 A1. Acomparable technique for the manufacture of ceramic dental components isdescribed for example in EP 1280475 B1. Going further into thistechnique in detail is therefore not required.

But with the prior art the easy production of flat products made ofceramic with a diameter of more than 20 mm is not possible, inparticular when the thickness is less than 1 mm. As an example dials ofwatches may be mentioned. But these can be prepared by the techniqueaccording to the invention without difficulty. On the other hand theredoes not exist in itself a need for the production of thin disk-shapedmetal products because such products can be easily stamped out of sheetmetal. However, the inventive method allows the production ofmechanically stable blanks for a CAD/CAM method. Such blanks areproduced according to WO 2011/023 490 A1 in a different,non-electrophoretic method. In that case the drying time of severalhours can be considered a disadvantage, although in the electrophoreticproduction immediately after the end of electrophoresis, there is astable product which can be immediately machined, and sintered.

PROBLEM TO BE SOLVED

It is therefore an object of the invention indicated in claim 1 and theapparatus based thereon, to enable a precise production of sinterable,flat blanks of metallic or ceramic slurry. Within that area in thecontext of the application are understood not only planar but alsoslightly curved objects, which may additionally be profiled (shaped) ona surface.

DESCRIPTION OF THE INVENTION

In the drawings:

FIG. 1 shows a vertical section through the machine according to theinvention ;

FIG. 2 shows the section in the plane AA of FIG. 1

In FIG. 1 is shown a part section through the device for carrying outthe invention. In a conductive container 1, which is connected to thenegative pole of a DC power source, there is an electrophoreticsuspension 2, which is kept in motion by an agitator 3 to prevent theformation of agglomerates. By means of a substrate holder 4, aprecipitation electrode 5, which is polarized positive, can be immersedin and moved out of the electrophoretic suspension. This device is notdifferent so far from the above mentioned prior art for the productionof tooth parts by electrophoresis.

New compared to the above technique is that the precipitation electrode5 is flat and its edge is covered by an insulating frame 6. In theembodiment of FIG. 2 of the description, the precipitation electrode 5can be acted upon from both sides.

With the apparatus shown, for example, ceramic discs with a diameter of30 mm and a thickness less than 1.5 mm of alumina can be produced. Forthis purpose, a precipitation electrode 5 from zinc sheet is clampedinto the frame 6 and electrophoretically coated. At a deposition time of180 seconds and a current of 35 mA, two slices of the desired size haveformed on the collecting electrode 5. The well known electrophoreticsuspension 2 requires, for a viscosity measurement, a necessary cycletime of 38 sec for a flow rate of 10 ml in a measuring funnel having adiameter of 2.3 mm. After coating, the alumina slice can easily be takenoff from the collecting electrode. The reason for this lies in the zincoxide layer that has been formed and which acts in the manner of aseparation layer. Subsequently, the blanks obtained are, as usual,sintered.

If the products to be manufactured should not be perfectly flat on bothsides, the collecting electrode can be coated on one side only. However,this opens up the possibility to produce curved products.

A further possibility of the invention exists to produce charactersraised or embossed on the slice, e.g. digits of a clock. For thispurpose, corresponding recesses or corresponding raised characters shallbe provided only in the surface of the collecting electrode.

The isolation of the collecting electrode at the edge of the frame 6 isessential to the invention, because the edge area of the electrode mustbe free of slurry for avoidance of drying cracks.

However, the invention can also be used for the production of metalingots. WO 2011/023490 A1 discloses a method for the production of toothparts from dental metal powder in which method a slurry is poured into amold and a stable blank is formed by drying in the mold, which blank isformed to a metallic tooth part by machining and sintering. These blanksmay have a diameter of 96 mm and a thickness of 20 mm. Such discs canalso be produced by electrophoresis, if the apparatus shown in FIGS. 1and 2 is dimensioned accordingly. A change in the slip composition ascompared to the prior art is not necessary.

LIST OF REFERENCE NUMERALS

-   1 container-   2 electrophoretic suspension-   3 stirrer-   4 substrate holder-   5 precipitation electrode-   6 frame

1. A process for the manufacture of a flat blank made of a metal orceramic slurry 2 by electrophoresis, characterized by covering an edgearea of a flat collecting electrode 5 with an insulating frame 6 duringthe electrophoresis.
 2. A method according to claim 1, characterized inthat the precipitation electrode 5 is coated on one or both sides.
 3. Amethod according to claim 2, characterized by using a collectingelectrode 5 made of zinc, and an alumina slurry as an electrophoresissuspension
 2. 4. A method according to claim 1, characterized by formingthe surface of the collecting electrode 5 with raised or recessedsymbols.
 5. A device for carrying out the method according to claim 1,with a container 1 filled with conductive electrophoresis suspension 2,which container is connected to the negative pole of a DC power source,wherein the suspension can be stirred by a stirrer 3 for the preventionof agglomerates, characterized by a positive polarity and verticallymovable substrate holder 4 that supports a frame 6 to cover the edgeportion of the collecting electrode
 5. 6. Apparatus according to claim5, characterized by a two-part frame
 6. 7. A method according to claim2, characterized by forming the surface of the collecting electrode 5with raised or recessed symbols.
 8. A device for carrying out the methodaccording to claim 2 with a container 1 filled with conductiveelectrophoresis suspension 2, which container is connected to thenegative pole of a DC power source, wherein the suspension can bestirred by a stirrer 3 for the prevention of agglomerates, characterizedby a positive polarity and vertically movable substrate holder 4 thatsupports a frame 6 to cover the edge portion of the collecting electrode5.
 9. Apparatus according to claim 8, characterized by a two-part frame6.
 10. A method according to claim 3, characterized by forming thesurface of the collecting electrode 5 with raised or recessed symbols.11. A device for carrying out the method according to claim 3 with acontainer 1 filled with conductive electrophoresis suspension 2, whichcontainer is connected to the negative pole of a DC power source,wherein the suspension can be stirred by a stirrer 3 for the preventionof agglomerates, characterized by a positive polarity and verticallymovable substrate holder 4 that supports a frame 6 to cover the edgeportion of the collecting electrode
 5. 12. Apparatus according to claim11, characterized by a two-part frame 6.